Process to obtain diesel from vegetable and animal oils through a hydrotreatment with short residence time and byproducts obtained from it

ABSTRACT

The invention relates to a method for obtaining diesel fuel from vegetable or animal oils through the addition of hydrogen in the presence of catalysts under suitable temperature and pressure conditions. The method is different from other similar methods in that it involves the use of space velocities of between 5.1 h-1 and 9 h-1, thereby enabling a reduction in the size of the reactor and in hydrogen consumption, as well as lowering construction and operating costs. The invention also relates to the products obtained using said method, which have demonstrated that in additions, even below 10%, they improve the performance of diesel engines, thereby lowering fuel consumption.

TECHNOLOGICAL SECTOR

The present invention explains a process consisting of the production of diesel fuel from vegetable or animal oils with the addition of hydrogen in the presence of catalysts at proper temperature and pressure conditions. This process differs from others in that the residence times are shorter which allows reducing the size of the reactor and the consumption of hydrogen, thus decreasing the equipment construction and the operation costs. Likewise, the byproducts obtained from this process are also part of this invention.

STATE OF THE ART

Nowadays, there is a trend focused on the use of alternative fuels for transportation, considering that the traditional source to obtain these fuels is petroleum, a non renewable resource that is gradually running out.

With the intention to set new options for the production of fuels, it has been proposed the production of diesel fuel from vegetable oils, which can be hydrogenated to produce paraffin rated within the diesel distillation range.

Alencar and et al, J. Agricultural Food Chemistry, Volume 31, No 6, 1268 to 1270, 1983, have shown that several fuels and industrial chemicals can be obtained from vegetable oils by simply changing the nature of the catalyst and the cracking process' temperature. Consequently, if calcium oxide is used as a catalyst, the product will consist of long-chain methyl ketones. On the other hand, if the catalyst is bentonite the main resulting product would be alquilbenzene.

In view of the above, there is a Canadian patent related with the production of a high performance diesel fuel obtained by hydrotreatment and from pure vegetable oils (U.S. Pat. No. 4,992,605). The process shows that the vegetable oils are put into contact with gaseous hydrogen at temperatures between 350° C. to 450° C. (662° F. to 842° F.) in the presence of a catalyst including cobalt-molybdenum or nickel-molybdenum, allowing the production of diesel which is separated from the mixture of the byproducts. This process is performed at space velocities of 0.5 h⁻¹ to 5 h⁻¹, where the space velocity is inverse to the reaction time, this is, the time during which the load is in contact with hydrogen and the catalyst and is expressed as the Liquid Hour Space Velocity (LHSV.)

Petrobras has filed patent application US 2006/0186020 for a process derived from the patent mentioned above which refers to the production of diesel obtained by hydrotreatment and from a mixture of vegetable oils and hydrocarbons. This process reports space velocities between 0.5 h⁻¹ and 2 h⁻¹.

In view of the above, application EP 1728844 was filed showing a procedure including the pre-treatment of the load to remove pollutants such as alkali metals, which may deactivate the catalyst. Again, space velocities within a range of 1 h⁻¹ to 4 h⁻¹ were mentioned.

Other types of oils used in these processes are reported in U.S. Pat. No. 5,705,722 which refers to a process to produce additives for diesel fuel with a high amount of ketanes that improve diesel properties. In said process, space velocities are between 0.5 h⁻¹ and 5 h⁻¹.

Other alternative to the process is reported in applications US 2007/0006523, U.S. Pat. No. 7,232,935 and WO2007/003709, where the linear paraffin obtained during the hydrotreatment of the vegetable oils are converted, using catalysts, into paraffin with linear chains by isomerization, thus improving the low temperature performance of the fuels obtained by hydrotreatment.

Application WO2006/100584 also pretends to solve the diesel stream problem at low temperatures and proposes hydrotreatment and isomerization of the vegetable oils in one single reactor. Space velocities handled in this process range between 0.5 h⁻¹ and 5 h⁻¹.

As it may be observed, the hydrotreatment processes mentioned before are performed at space velocities ranging between 0.5 h⁻¹ and 5 h⁻¹, which are the normal LHSV used in the oil industry. The applicant has surprisingly found that being the vegetable and animal oils from a source different to the hydrocarbons, they show a different reactivity that permits exploring other space velocity ranges, which is the main concern of the present invention.

Consequently, there is a need for new processes in the state of art to reduce the residence time and allow the reduction of the reactors sizes while the consumption of hydrogen per liter of oil decreases and the production of high-performance products is assured, when they are used as components for diesel engines fuels.

DESCRIPTION OF THE INVENTION

The process herein claimed exceeds the existing outcome of the state of the art. For instance, a reactor capable of processing 2,000 liters per day using the current technology of the state of the art could process 12,000 to 15,000 liters per day of pure vegetable or animal oil using the technology proposed in the present invention, reducing up to a 40% the consumption of hydrogen with respect to the amount required by the other technologies

In general, the process claimed comprises the heating, reaction, decantation separation and, a prior discretional stage of mixing oils and hydrocarbons and/or a distillation separation stage, as it is shown in FIG. 1. The sequence of steps featured with the invention is explained as it follows:

-   -   1. Heat up the vegetable or animal oil in a furnace at the         reaction temperature of 280° C. to 450° C. (536° F. to 842° F.)         depending on the quality of the catalyst and the composition of         the load. The exact temperature for this part of the process is         determined empirically for a given system, increasing the         temperature of the load until the desired quality of the product         is achieved.     -   2. Pass the oil from stage one through a reactor filled with a         catalyst composed of a porous solid material with deposits of         active metallic sulphurs on its surface. There, the         hydrotreatment reaction happens at a temperature between 280° C.         and 450° C. (536° F. to 842° F.) a pressure between 5.0 MPa and         15 MPa, space velocity between 5.1 h⁻¹ and 9.0 h⁻¹, and a         relation of hydrogen per load between 178 L of H₂ per liter of         oil and 534.3 L of H₂ per liter of oil, which surprisingly allow         the reactions transforming oil into the desired products on the         range of diesel to be performed, with a shorter residence time         and a reduction in the consumption of hydrogen of as much as a         40%.     -   3. Recover the product from the previous stage in closed         containers and separate them by decantation into three phases:         water, oil, and gases. These streams are physically separated by         means of well-known and widely used techniques in the industry.         The gases obtained can be used as fuel in the refinery or can be         separated and purified to recover the hydrogen, which is         recirculated.

FIG. 1 shows the streamchart of the process; where upon the diesel (1) and oil (2) storage stream (3) is pumped having the desired composition. The mixture obtained is then combined with hydrogen (8) and passes through a heating (4) and subsequent reaction process (5) where the products are transformed and then separated in stages (6 and 9). The hydrogen stream can recirculated after being purified (7) and compressed (8). The separation (6) produces diesel (A) and water (B).

In an embodiment of the invention, the vegetable or animal oil can be used as raw material in a 100% pure stream or in mixtures with hydrocarbons coming from petroleum ranging between 0 and 99% in volume. In this last case, the process comprises a previous additional stage before the heating process, which consist on mixing both the vegetable oil stream and the hydrocarbons stream, which is to be done in line at a temperature such to make the vegetable oil acquire the necessary fluidity to mix with the hydrocarbon load.

Other embodiment of the invention includes a distillation separation stage at the end of the process, performed by means of the traditional procedures, to separate the streams depending on the boiling point. It is preferred to include this stage in separation processes with space velocities above 7.5 h⁻¹.

In extreme cases, at space velocities near to 9 h⁻¹, a bottoms material that did not react can be obtained; such material is recovered by distillation and is recirculated to start the process from stage 1. In any case, recirculating does not eliminate the benefit of hydrotreating a larger load volume per reactor volume.

Now, in a preferred embodiment the second stage catalyst comprises a porous alumina support impregnated with metallic Ni and Mo or of Ni and Co sulphurs.

The great advantage of this invention is that the hydrotreatment process of the vegetable oils under these conditions allows having short reaction times, which make it possible to work with smaller reactors than those traditionally used for specific loads, when compared to the reactors required for the existing processes. This affects directly the building costs of these plants which, by operating at high pressures, require specialized materials and production techniques increasing the prices considerably depending on the size of the reactor.

Moreover, the hydrogen consumption is optimized due to shorter reaction times than those reported for conventional processes, as the development of undesired reactions in the production of diesel fuel that consume hydrogen—the most expensive raw material of the process—is controlled.

The reduced residence times in the reactor allow the vegetable oil stream to be added at an intermediate part of the catalytic bed, as it is shown on FIG. 2, allowing the catalyst upstream to be protected from the gasses generated by the reactions of the vegetable and animal oils, such as CO and CO₂, which contaminate the catalyst. Therefore, a variation embodiment of the invention comprises the addition of vegetable oil directly into an intermediate part of the reactor or between reactors when the process is performed using several reactors in series.

Similarly, the low residence times also originates another embodiment of the invention in which the reaction stage (5) is performed in the tubular reactors, which in some cases may be integrated to the furnace (4) in such a way that the tube inside the furnace is filled with the catalyst (4/5) eliminating the need of a separate equipment to perform the reactor's function, as it is shown in FIG. 3.

Furthermore, is a part of the invention claimed herein the products obtained from the process defined above, which have shown that in additions, even under 10%, they improve the performance of Diesel engines, especially reducing the consumption of fuel.

Next, we show some examples of the best way to carry out the invention. These examples are illustrative and by no means pretend to limit the scope of the invention.

Examples

Tests were performed at the pilot plant with pure palm oil, at space velocities between 6.6 h⁻¹ and 8.0 h⁻¹, using a conventional catalyst for hydrotreatment of paraffins, in order to obtain a main product within the distillation range of Diesel.

The pilot plant test conditions are shown on Table 1.

TABLE 1 Operation conditions for the tests performed at the pilot plant. Space Velocity Temperature Pressure H₂ LN/ Consumption h⁻¹ (° C.) (MPa) load oil L of H₂ LN/oil L 2 350 9 471 354 6.6 413 9 277 258 8 400 9 208 195

The run performed at a space velocity of 2 h⁻¹ was done as a reference to compare it with the known processes. It can be seen that insofar as it is performed at higher space velocities and a lower relation between hydrogen and load streams, the consumption of hydrogen decreases favoring the fuel production costs.

Table 2 shows a comparison of the characteristics of the fuels obtained through hydrotreatment of the palm oil at different space velocities, and are compared to those of a diesel extra (DE).

TABLE 2 Properties of Diesel and of the vegetable oil hydrotreated at different LHSV. Hydrotreated Hydrotreated Hydrotreated crude oil (CO) crude oil (CO) crude oil (CO) Properties Units DE LHSV: 2 h⁻¹ LHSV: 6 h⁻¹ LHSV: 8 h⁻¹ Cetane Ketanes 50.3 95.7 98.1 92.0 number Density g/ml 0.847 0.785 0.782 0.7896 Flash point ° C. 66 96 20 13 Cloud point ° C. −2 26 20 22 Fluidity point ° C. −6 18 15 18 Heat of MJ/Kg 45.764 46.889 46.966 46.492 Combustion Ashes % p <0.001 0.013 <0.001 <0.001 Acidity mgKOH/g 0.001 <0.10 7.105 Corrosion of 1A 1A 1A 1A Cu

It is notorious the difference in the Cetane number, which are highly superior for the fuels obtained by hydrotreatment of palm oil; even when this is obtained at very high space velocities, which make these products very attractive to be part of a commercial fuel. For high space velocities it can be seen an increase in the cloud point, fluidity point, and acidity, as well as a reduction of the flash point under the same conditions. These properties can be adjusted through dilution with appropriate streams such as diesel obtained from petroleum.

Table 3 shows the characterization of mixtures at different proportions of high quality Diesel with fuels obtained from palm oil at high space velocities. The characteristics of the mixtures are similar to those of the high quality diesel.

TABLE 3 Properties of hydrotreated diesel-oil mixtures at different space velocities and different proportions. Mx 3% CO- Mx 5% CO- Mx 10% CO- Mx 3% CO- Mx 5% CO- Mx 10% CO- DE LHSV: DE LHSV: DE LHSV: DE LHSV: DE LHSV: DE LHSV: Test DE 6 h⁻¹ 6 h⁻¹ 6 h⁻¹ 8 h⁻¹ 8 h⁻¹ 8 h⁻¹ Cetane 50.3 50 51 52.6 50.1 50.4 51.9 number Density (g/ml) 0.8477 0.833 0.8316 0.8293 0.8331 0.8324 0.8309 Flash point 66 60 61 59 61 61 60 (° C.) Cloud point −2 −2 −1 −1 −1 −2 −2 (° C.) Fluidity point −6 −12 −12 −12 −12 −12 −12 (° C.) Heat of 45.764 45.655 45.321 45.659 45.647 45.697 45.610 combustion (MJ/Kg) Corrosion of 1A 1A 1A 1A 1A 1A 1A Cu

It is observed that all the characteristics of the mixtures are similar to those of the diesel (DE) obtained from petroleum.

Test in Engines of the Hydrotreated Diesel-Palm Oil Mixtures Obtained at High Space Velocities

To learn the behavior of the fuel obtained and of the combinations with high quality Diesel (DE), tests were performed on an experimental Cummins 160, model 1998, Diesel engine, in compliance with standard SAE J1349.

The results obtained are shown on table 4. Results of the tests with high quality Diesel (DE) and methyl ester (biodiesel) are also illustrated on this table. This fuel is produced by the transesterification of vegetable oils.

TABLE 4 Power, torque, and fuel consumption of a diesel cycle engine with different fuels and mixtures. 30%/ 20%/ 10%/ 5%/ 3%/ 10%/ 5%/ 3%/ DE ME 2 h⁻¹ 2 h⁻¹ 6 h⁻¹ 6 h⁻¹ 6 h⁻¹ 8 h⁻¹ 8 h⁻¹ 8 h⁻¹ Maximum 543.9 540.1 554.2 558.0 557.2 546.8 557.5 555.3 556.2 563.9 Torque (NM) Maximum 120.3 121.3 124.8 124.7 124.0 124.2 125.5 123.9 126.7 127.2 Power (KW) Fuel 254.7 267.1 241.8 248.5 235.0 233.2 231.4 236.0 231.3 230.0 Consumption (g/kwh) 20%/2 h⁻¹: Mixture of 20% vegetable crude oil hydrotreated at LHSV: 2 h⁻¹, and 80% Diesel 30%/2 h⁻¹: Mixture of 30% vegetable crude oil hydrotreated at LHSV: 2 h⁻¹, and 70% Diesel 10%/6 h⁻¹: Mixture of 10% vegetable crude oil hydrotreated at LHSV: 6 h⁻¹, and 90% Diesel 3%/6 h⁻¹: Mixture of 3% vegetable crude oil hydrotreated at LHSV: 6 h⁻¹, and 97% Diesel 10%/8 h⁻¹: Mixture of 10% vegetable crude oil hydrotreated at LHSV: 8 h⁻¹, and 90% Diesel 5%/8 h⁻¹: Mixture of 5% vegetable crude oil hydrotreated at LHSV: 8 h⁻¹, and 95% Diesel 3%/8 h⁻¹: Mixture of 3% vegetable crude oil hydrotreated at LHSV: 8 h⁻¹, and 97% Diesel

Table 4 demonstrates that the tests performed with mixtures of fuels obtained from mixing diesel and palm oil hydrotreated at high space velocities offer less fuel consumption, even at low additions of oil hydrotreated at high space velocities. 

1. A process to produce diesel from vegetable or animal oils by a hydrotreatment process comprising the following stages: a. Combine hydrogen with pure vegetable or animal oil or with a mixture of these oils with hydrocarbons. b. Heat up the mixture of stage a) in a furnace at reaction temperature, between 280° C. and 450° C. (536° F. to 842° F.). c. Pass the oil from stage b) through a reactor filled with a catalyst composed by a porous solid material containing active metallic sulphurs deposited on its surface. Here the hydrotreatment reaction happens at temperatures between 280° C. and 450° C. (536° F. to 842° F.), pressures between 5.0 MPa and 15 MPa, space velocities between 5.1 h⁻¹ y 9.0 h⁻¹ and a ratio of hydrogen per oil load between 178 NL of H₂ per liter of oil and 534.3 NL of H₂ per liter of oil. d. Recover the product from the previous stage in closed containers and separate it by decantation in 3 phases: water, oil, and gasses.
 2. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 1, in which the vegetable or animal oil can be used in mixtures with hydrocarbons from petroleum in mixtures ranging from 0 to 99% in volume.
 3. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 2 characterized in that if the oil is a mixture, the process comprises a previous additional stage before the heating stage, consisting of combining the vegetable or animal oil stream and the hydrocarbons stream, which is performed in line at the temperature at which the vegetable or animal oil acquires the appropriate fluidity to mix itself with the hydrocarbon load.
 4. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 1 characterized in that it includes a distillation separation stage at the end of the process.
 5. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 4, characterized in that the inclusion of the distillation separation stage is preferred for processes with space velocities higher tan 7.5 h-1.
 6. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 5, characterized in that the material that does not react is recovered through distillation and is recirculated to make it start the process all over again, from stage a).
 7. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 1, characterized in that the gases obtained from the decantation separation stage b) are recovered, purified, and recirculated.
 8. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 1, characterized in that the catalyst from the second stage comprises, preferably, a porous alumina support impregnated with Ni and Mo or Ni and Co metallic sulphurs.
 9. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 1, characterized in that the vegetable or animal oil stream is added at an intermediate portion of the catalytic bed.
 10. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 9, characterized in that the vegetable or animal oil stream may be added at an intermediate part of the catalytic bed without prior warming.
 11. A process to obtain diesel from vegetable or animal oils through hydrotreatment according to claim 1, characterized in that the reaction stage c) happens in tubular reactors integrated to the furnace in a way such that the furnace tube fills up with catalyst.
 12. The product obtained through the process defined in any of the previous claims.
 13. A fuel comprising a mixture of the product described in claim 12 and diesel produced from hydrocarbons. 